3 months ago I purchased a 91 Camaro 350 Z28. 3 weeks later it started running rich and it idled rough. I have reciepts for everything new on the car. I have just put in new injectors, plugs and just last week the guy I bought the car from helped me tear down the engine all the way to the new shortblock so I could get a valve job. It's back together and running, but it's still running rich and rough. It has been HELL not being able to drive this specimen for 2 months. Anyone with any experience with this problem who has any ideas or answers would be greatly appreciated. I'm running out of options.

 

What's the fuel pressure? If the vacuum line to the regulator is cracked, or if the regulator is bad, pressure will be excessive and it will run rich.

 

Also may want to try to replace the Oxygen Sensor with a brand new Bosch unit. Check the intake for "leaks" by spraying carb cleaner at all the seams and see if the idle changes. If so, you have an inake leak.

 

Instead of replacing parts needlessly, why not get a Tech1 and scan the parameters of the system. Then at least you know where to go.....Can't get a Tech1? Usually a dealer will scan the system and operating parameters for about $25.........

 

Thanks, I'll check it out. But what about the EGR valve, has anyone had problems with it in the past?

 

check your mass air flow sensor and relay, if there is anything changing the turbulence of the air entering the sensor, like a leaf or paper, or somehting, the maf will show an incorrect ratio of air and will richen the mix. if your relay for the maf is bad, the ecm will get bad signals about the mix, and richen the mix. also check your air filters and air flow from intake forward, as these can easily be partially clogged by road degree.

 

I'm not trying to be a dick here, but he doesn't have a MAF, so this info is useless; provided he is running the stock speed density system which uses MAP. They stopped using the MAF system in 89 I believe.

Have you checked your IAC and reset it yet? What is your TPS voltage? It should be around .54v +/- .07v. Get the fuel pressure. Check the injector resistance, should be around 14-17ohms just to be sure, even though they are new. Does it idle like this just in P and N or when the engine is under load as in D or R? you can also hook up a volt meter to your O2 sensor to see just how rich it is running. Here's how:

Adjusting your fuel mixture Via your O2 sensor and Digital volt meter
Thought you needed an expensive scanning device such as AutoXray or Diacom to view your O2 sensors voltage readings? Think again! You NEED to do this if you have an adjustable fuel pressure regulator or if you have a Q-jet equipped thirdgen and are changing the metering rods to achieve optimal performance.
You will need: A digital voltage meter, approximately ten feet of wire preferebly 12 gauge or smaller, wire connectors (Screw type "european" connectors preferebly), Jack, jackstand, wire strippers.
Step One: Disconnect negative battery cable
Step Two: Jack up vehicle on drivers side
Step three: Locate plastic connector for the O2 sensor near exhaust manifold, Disconnect.
Step four: Strip end of materials wire approx. 2 inches to expose core
Step five: Put exposed end into one end of the weather pack connector for the O2 sensor and reconnect.. Its a tight fit and you might have to trim or expose some more wire. It also might take a little force for it to snap backtogether.
Step six: Route wire away from exhaust manifolds or headers back into passenger compartment. If you plan on using this tuning aid temporarily simply route through door jamb. If not, there is a hole under the power booster in which you can route the wire.
Step Seven: Once inside of engine compartment trim wire to an accessable length. Connect wire to the positive probe of your Digital volt meter MAKING SURE that no part of the wire is exposed in any way so as to not ground the o2 sensor accidentally. European wire connectors worked well for me (the kind with a screw in each end to hold the wire in a plastic connector. Avail. at radio shack)
Step eight: Use the extra length of wire to make a ground for the Digital volt meter. Under the dash there are plenty of places to ground the wire. Connect it to the negative probe of the digital volt meter.
Step Nine: Lower car, reconnect battery. Start car and turn your Digital volt meter on.
The range is as follows 3mV being the leanest, 1V being the richest. Part throttle does not matter so much as the computer always keeps it somewhere in this range depending several on variables and inputs from other systems sensors. At Wide open throttle the MOST desireable voltage should USUALLY be somewhere between .850mV an .900mV Make adjustments accordingly to reach the desired settings. Remember, the lower the voltage the leaner, the higher the voltage the richer. This also has an effect on spark timing. For instance if your car was running lean prior to adjustment and you had the base timing set to just before knock you may be able to adjust your timing for more advance with more fuel. The same is true vice versa. In addition, if you have an old O2 sensor take this opportunity to replace it as an O2 sensors sensitivity greatly diminishes with increased mileage.
It is imperative that you DO NOT ground the O2 sensor wire. This will KILL your O2 sensor.

Hope all of this helps. This is a tech article from thirdgen.org so it is good.